Apparently it's pronounced 'sheed tzeeooo'. (Hard writing it!) But yeah, I pronounce it 'shit zoo' myself, but in the NSC spirit of deconstructing the Joke de Jour threads I went all pretentious.
I had to think about this 'joke' for a second before I realised that it only works if you mispronounce shih tzu as 'shit zoo' rather than using the correct pronunciation.